1. Field of the Invention
The present technical solution belongs to the area of altering physical properties by means of deformation, which follows the heat treatment used in manufacturing cylindrical bodies.
2. Description of the Prior Art
In technical applications, one benefit of hollow bodies is the better utilization of weight of the material for providing functional properties. In addition to those hollow bodies, in which the cavity is a necessary condition for their function, and which find use in, for example, pipes, pressure vessels, boilers, heat exchangers, springs and other structures, there are a growing number of applications where the primary purpose of the cavity is to save weight and reduce the moment of inertia. Hollow rotating shafts may serve as an example. They are much lighter than solid shafts of identical shape.
Yet, hollow shafts can transmit torque equal to that of solid shafts with identical outer dimensions. In addition, their acceleration and deceleration require much less energy, owing to their low moment of inertia. The better the mechanical properties of the material, the thinner the wall can be—and the higher the efficiency of the mass of the structural element.
Stock for making hollow steel bodies must be first converted to the required shape of the intermediate product and then heat treated to obtain excellent properties including high strength and sufficient toughness. The shape of such intermediate product can be obtained by various methods, e.g. machining, forming, welding or by other techniques.
The weakness of the method which, up to this date, has been used for making hollow bodies or their intermediate products is that it is problematic, technically demanding, complicated in materials terms and costly in achieving the shape and optimum properties. Moreover, the conventional machining methods produce large quantities of waste in the form of chips. Conventional combinations of forming methods or other methods with subsequent additional treatment require multiple heating operations, leading to higher overall energy consumption.